CHAPTER 1
INTRODUCTION
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IIT Kharagpur
The advancem ent o f i n t e g r a t e d c i r c u i t t e c h n o lo g y h as b ro u g h t- in phenom enal changes in the d e s ig n , p r o d u c t io n and m a in te n an c e o f d i g i t a l s y s te m s . W it h the e v e r - i n c r e a s i n g d e n s i t y o f c i r c u i t p a c k a g in g , the problem s o f f a u l t d i a g n o s i s h av e t a k e n new d im e n s io n s . H i g h e r p a c k a g in g d e n s i t y h as
s u b s t a n t i a l l y i n c r e a s e d the amount o f c i r c u i t in fo r m a t io n t o be s t o r e d for the p u rpo se o f f a u l t d i a g n o s i s . The r e s t r i c t i o n on th e pin- count o f t h e s e h i g h d e n s i t y c h i p s h as c o n s i d e r a b l y r e d u c e d the acc ess to th e i n t e r n a l l i n e s of the c i r c u i t . As a r e s u l t , th e o v e r a l l c o n t r o l l a b i l i t y and o b s e r v a b i l i t y o f th e n etw o rk im plem ented on a c h ip has g r e a t l y r e d u c e d . T h i s r e d u c t i o n n e c e s s i t a t e d e x t e n s i v e p r o c e s s i n g o f t h e in fo r m a t io n
c o l l e c t e d d u r in g a fa u l t - d i a g n o s is e x p e r im e n t . C o n s e q u e n t l y , th e c o m p le x it y o f t e s t g e n e r a t io n a n d t e s t e x e c u t i o n hav e g r e a t l y i n c r e a s e d . The c o s t o f t e s t i n g g r a d u a l l y form ed s i z a b l e p o r t io n o f th e p ro d u c t d e v elo p m en t, m a n u fa c t u r in g a nd m a in te n a n c e c o s t s . In v ie w o f t h i s s i t u a t i o n , c o n s i d e r a b l e a t t e n t i o n is p a i d to t h e fo r m u la t io n and im p le m e n t a t io n o f
e f f i c i e n t t e s t g e n e r a t i o n a lg o r it h m s and d i a g n o s t i c p r o c e d u r e s . The e m p hasis is d i r e c t e d to w ards r e d u c t i o n o f the c o s t in
term s o f d i a g n o s t i c in fo r m a t io n s t o r a g e and t h e a s s o c i a t e d c o m p u t a tio n a l e f f o r t . U l t i m a t e l y , i t is deem ed n e c e s s a r y t o
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IIT Kharagpur
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pay due a t t e n t io n to d e s i g n t h e c i r c u i t s such t h a t t h e y are t e s t a b l e w i t h i n a s t i p u l a t e d c o s t c o n s t r a i n t .
The m a jo r f u n c t io n s o f a f a u l t d i a g n o s i s p r o c e d u r e are ( i ) a n a l y s is of the netw ork b e h a v io u r and g e n e r a t i o n o f a t e s t - s e t , ( i i ) t e s t a p p l i c a t i o n , and ( i i i ) p r o c e s s the t e s t r e s p o n s e fo r d e t e c t i o n /l o c a t i o n o f f a u l t s . T h e s e fu n c t io n s in v o l v e a l a r g e number o f t a s k s s u c h as f a u l t m o d e ll in g , s i m u l a t i o n , t e s t a b i l i t y a n a l y s i s and t e s t g e n e r a t i o n , test- s e t o p t i m i z a t i o n , f a u l t l o c a t i o n e t c . A r e v ie w o f the s t a t e o f a r t C o u t l i n e d in th e s u b se q u e n t c h a p t e r s ) r e v e a l s t h a t w id e - r a n g in g m eth o d o lo g ies h ave be e n p ro p o se d to h a n d l e e ac h o f t h e s e t a s k s . F u r t h e r , the netw o rk m o d e l l in g and a n a l y s i s v a r i e d c o n s i d e r a b l y f o r each o f t h e s e t a s k s . In t h i s b a c k g r o u n d , it is f e l t n e c e s s a r y to e v o lv e a model b e s t s u i t e d to h a n d l e a l l t h e s e t a s k s w i t h u n i f o r m i t y and c o n s i s t e n c y . W ith t h i s o b j e c t i v e as one o f t h e prim e c o n s i d e r a t i o n s , a g r a p h - t h e o r it ic model term ed as " D i a g n o s t i c L o g ic Grap h ( D L G )"
is p ro p o se d in the p r e s e n t w o r k . T h e DLG m odel is u s e d in c o n j u n c t i o n w ith s ix - v a l u e d l o g i c fo r c i r c u i t - l e v e l f a u l t d i a g n o s i s . T h r o u g h o u t the w ork, s t u c k f a u l t s o f p erm an en t n a t u r e are c o n s i d e r e d in c o n n e c t io n w it h i r r e d u n d a n t l o g i c n e t w o r k s . U s in g t h i s s i n g l e m odel, f o l l o w i n g a s p e c t s o f
f a u l t d i a g n o s i s are d e a l t w it h in the p r e s e n t work - true- v a l u e s i m u l a t i o n , f a u l t c o v e r a g e e v a l u a t i o n , c o m p u t a tio n o f m i n i m a l /n e a r l y m in im al t e s t - c o u n t , a d a p t iv e t e s t g e n e r a t i o n ,
f a u l t l o c a t i o n , and, t e s t a b l e d e s i g n o f d i g i t a l n e t w o r k s .
T h i s s i n g l e model u s e d f o r t h e r e p r e s e n t a t i o n o f c o m b i n a t i o n a l
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IIT Kharagpur
c i r c u i t s is a d a p te d to h a n d le s e q u e n t i a l c i r c u i t s and MOS
c i r c u i t s . F u r t h e r , same DLG model is e x t e n d e d t o h a n d l e system- l e v e l f a u l t d i a g n o s i s . The f o l l o w i n g p a r a g r a p h s b r i e f l y o u t l i n e t h e c o n te n ts p r e s e n t e d in th e s u b se q u e n t c h a p t e r s .
The C h a p te r 2 d e a ls w it h c o m b in a t io n a l c i r c u i t s . F o ll o w in g a b r i e f r e v ie w o f s t a t e o f a r t f o r t e s t g e n e r a t i o n and f a u l t s im u l a t io n , the new DLG model is i n t r o d u c e d . Based on v a r io u s p r o p e r t i e s o f t h i s m odel, a p r o c e d u r e is d e s c r i b e d to p erfo rm true- v alue s i m u l a t i o n . L a t e r , a method o f fault- c o v e r a g e e v a l u a t i o n is f o r m u la t e d . T h is e l i m i n a t e s the u sa g e and m ain ten an ce o f e x h a u s t iv e f a u l t - d i c t i o n a r i e s and s t u d y o f f a u l t - c o l l a p s i n g a s p e c t s t h a t are c o n s i d e r e d fo r c o n v e n t io n a l f a u l t s im u l a t io n m e th o d s. F o l lo w in g t h i s , c o m p u ta tio n o f te st- s e t s i z e is d e s c r i b e d u s i n g the co n c e p ts o f t e s t - c o u n t . Two s i n g l e - f a u l t d e t e c t i o n t e s t- s e t g e n e r a t i o n p ro c e d u r e s are
p r e s e n t e d c o n s i d e r i n g the p a t h - s e n s i t i z a t i o n p r i n c i p l e s , b a s e d on ( i ) test- co u n t f o r the c i r c u i t , and, ( i i ) a d a p t iv e t e s t g e n e r a t i o n w ith a s t a r t - s m a ll approach u s i n g t e r m in a l- s t u c k
f a u l t d e t e c t io n t e s t - s e t . F u r t h e r , m u l t ip le - s t u c k f a u l t l o c a t i o n a sp e c ts are d i s c u s s e d w it h r e f e r r e n c e to a c h i e v i n g f o r c e d c o n s i s t e n c y in o b s e r v e d r e s p o n se and f o r m a t io n o f
f a u l t m a t r i c e s . L a s t l y , the o r d e r o f c o m p l e x it y in v o l v e d fo r th e c o m p u ta tio n o f v a r io u s p r o c e d u r e s f o r m u l a t e d in t h e
c h a p t e r is d i s c u s s e d . Some o f t h e s e b a s i c p r o c e d u r e s are u s e d in th e l a t e r c h a p t e r s .
In C h a p t e r 3, th e DLG c o n c e p t s are e x t e n d e d fo r r e p r e s e n t a t i o n o f s e q u e n t i a l c i r c u i t s . T e s t g e n e r a t i o n fo r
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IIT Kharagpur
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s i n g l e - f a u l t d e t e c t i o n and l o c a t i o n o f m u lt ip le - s t u c k f a u l t s are d e a l t w i t h . C h a p t e r 4 d i s c u s s e s the u s a g e o f DLG fo r MOS c i r c u i t t e s t i n g . S w it c h in g d e v ic e f a u l t s and c h a r g e r e t e n t i o n co n cep ts are a p p r o p r i a t e l y r e p r e s e n t e d and a solu- tio n - grap h is d e v e lo p e d out o f DLG to g e n e r a t e s t i m u l i for i n i t i a l i z a t i o n and t e s t i n g p u r p o s e s . An a d a p t iv e t e s t g e n e r a t i o n p ro c e d u re is fo r m u la te d to c o v e r a l l t y p e s o f s t u c k f a u l t s c o n c e r n in g t r a n s i s t o r s , b u s - lin e s , and, p rim ar y - in p u t/p r im a r y - o u tp u t l i n e s .
In C h a p ter 5 , t e s t a b l e d e s ig n of c o m b in a t io n a l c i r c u i t s is d i s c u s s e d . A g e n e r a l method o f m o d i f i c a t i o n o f c i r c u i t s to a c h ie v e tw o - p attern t e s t a b i l i t y is in t r o d u c e d c o n s i d e r i n g te r m in a l- stu c k f a u l t s . A l s o , im p le m en tatio n o f adhoc m o d i f ic a t io n s fo r c e r t a i n c i r c u i t s i s d i s c u s s e d on c a s e t o c a s e b a s i s f o r r e d u c t i o n o f t e r m in a l- s t u c k f a u l t t e s t - s e t s i z e . F u r t h e r, p lac em en t o f t e s t - p o in t s and a p a r t i t i o n i n g s t r a t e g y fo r g e n e r a t i o n o f a t e s t - s e t w it h r e d u c e d s i z e is i n t r o d u c e d . T h i s is done w i t h a v ie w to p r o v id e c o m p lete i n t e r n a l f a u l t c o v e r a g e . A d i v i d e and c o n q u e r t e s t i n g stra- t e g y i s , n e x t , p r o p o s e d fo r m u l t i p l e - f a u l t d e t e c t i o n o f
c i r c u i t s u s i n g s i n g l e - f a u l t d e t e c t i o n t e s t - s e t . A d a p t a t i o n o f DLG fo r system - level f a u l t d i a g n o s i s i s r e v i e w e d at C h a p t e r 6 . A d e s ig n fo r in t e r c o n n e c t i o n l i n k s o f a d i s t r i b u t e d system netw ork i s fo r m u l a t e d . D i s t r i b u t e d d i a g n o s i s a l g o r i t h m is d e v e lo p e d fo r t h i s n e t w o r k to l o c a t e f a u l t y
m o du les p r o v id e d t o t a l num ber o f f a u l t y m o du les in t h e sy stem does not e x c e e d a s p e c i f i e d l i m i t .
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IIT Kharagpur
fo r f a u l t m o d e lin g and s im u l a t io n o f d i g i t a l n etw o rks i n c l u d in g MQS c i r c u i t s and system l e v e l d i a g n o s i s . The same metho
d o lo g y is u s e d fo r t e s t a b l e d e s ig n of c i r c u i t s . C o n s id e r a b l e a d v a n tag e i s d e r i v e d by u s i n g DL graph w it h r e s p e c t t o u n i f o r m i t y i n t r e a t m e n t o f a l l a sp e c ts o f f a u l t d i a g n o s i s such as s im u l a t i o n , t e s t g e n e r a t io n , f a u l t c o verage e v a l u a t i o n and f a u l t l o c a t i o n .
